Zinc alloy plated steel material having excellent surface quality and corrosion resistance, and method for manufacturing same

ABSTRACT

Provided is a plated steel material which can be used for an automobile, a household appliance, a building material, and the like and, more specifically, to a zinc alloy plated steel material having excellent surface quality and corrosion resistance, and a method for manufacturing the same.

TECHNICAL FIELD

The present disclosure relates to a plated steel material that can beused in an automobile, a household appliance, a building material, andthe like, and more particularly, to a zinc alloy plated steel materialhaving excellent surface quality and corrosion resistance, and a methodfor manufacturing the same.

BACKGROUND ART

A zinc plating method for inhibiting the corrosion of iron by a cathodeprocess has been widely used to manufacture a steel material having highcorrosion resistance, due to its excellent corrosion resistanceperformance and economic efficiency. In particular, a hot-dip galvanizedsteel material, forming a plating layer by immersing a steel materialinto molten zinc, has a relatively simple manufacturing process andrelatively low product costs, compared to an electro-galvanized steelmaterial, and, thus, demand for such hot-dip galvanized steel materialfor automobiles, household appliances, building materials, and the like,is increasing.

The hot-dip galvanized steel material may have characteristics ofsacrificial corrosion protection, in which zinc having relatively lowoxidation-reduction potential is first corroded to inhibit corrosion ofthe steel material, compared to iron, when exposed to a corrosiveenvironment. In addition, the hot-dip galvanized steel material mayimprove corrosion resistance of the steel material, since the zinc of aplating layer is oxidized to form a dense corrosion product on a surfaceof the steel material, to block the steel material from an oxidizingenvironment.

However, air pollution and deterioration of a corrosive environment areincreasing due to the advancement of industry, and a need for thedevelopment of a steel material having better corrosion resistance,compared to conventional galvanized steel, is increasing, due to strictregulations on resource and energy saving. As a part of these issues,various studies into a technology of manufacturing a zinc alloy-basedplated steel material have been conducted to improve the corrosionresistance of the steel material by adding elements such as aluminum(Al) and magnesium (Mg) to a zinc plating bath. As a representative zincalloy-based plated steel material, studies have been actively conductedinto a technology of manufacturing a Zn—Al—Mg-based plated steelmaterial in which Mg is additionally added to a Zn—Al platingcomposition system (Patent Document 1).

Many of the plated steel materials used in the industry may be oftensubjected to various processes such as cutting, bending, tensioning, andthe like, to be manufactured as final products. In this case, cutsurfaces or processed surfaces may have problems in that corrosionresistance maybe deteriorated due to exposure of a base iron or damageto the plating layer. In particular, in a Zn—Al—Mg-based alloy plating,processed surfaces may be more vulnerable because the plating layer maybe more brittle, compared to a conventional zinc plating. Previously,there have not been many studies into improvement of the corrosionresistance of a processed portion.

(Patent Document 1) Japanese Patent Publication No. 2002-332555

DISCLOSURE Technical Problem

An aspect of the present disclosure is to provide a zinc alloy platedsteel material having excellent surface quality and excellent corrosionresistance in a cross-sectional portion, as well as excellent corrosionresistance in a processed portion, and a method of manufacturing thesame.

The problems to be solved by the present disclosure are not limited tothe problems mentioned above, and other problems not mentioned will beclearly understood by those skilled in the art from the followingdescription.

Technical Solution

According to an aspect of the present disclosure, a zinc alloy platedsteel material having excellent surface quality and corrosionresistance, includes: a base iron; a zinc alloy plating layer formed onthe base iron; and an inhibition layer formed between the base iron andthe zinc alloy plating layer, wherein a Zn phase of a surface of thezinc alloy plating layer comprises 15 to 90 area %, and the inhibitionlayer includes a ternary alloy phase layer of Zn/MgZn₂/Al having athickness of 2 μm or less on the inhibition layer, wherein the ternaryalloy phase layer comprises 30 to 90 area % of a surface of theinhibition layer.

According to another aspect of the present disclosure, a method ofmanufacturing a zinc alloy plated steel material having excellentsurface quality and corrosion resistance, includes: preparing a baseiron; immersing the base iron into a zinc alloy plating bath containingMg and Al to plate the base iron; and wiping the plated base iron, andthen cooling, wherein the cooling satisfies the following relationship1:

0.7Vc≤Vc′≤1.5Vc   [Relationship 1]

where Vc is an average cooling rate until end of solidification of aplating layer immediately after wiping, and Vc′ is an average coolingrate until the start of solidification of the plating layer immediatelyafter wiping.

Advantageous Effects

According to an aspect of the present disclosure, a zinc alloy platedsteel material having excellent surface characteristics by preventingdiscoloration of a surface of a plating layer, and having excellentcorrosion resistance not only in a cross-sectional portion but also in aprocessed portion, and a method for manufacturing the same, may beprovided. Therefore, there is an advantage in that it a usage area maybe broadened to an area to which a conventional usage is limited.

DESCRIPTION OF DRAWINGS

FIG. 1 is a photograph showing a cross-section of a plating layer ofInventive Example 3, among Examples of the present disclosure.

FIG. 2 is a photograph showing a cross-section of a plating layer ofComparative Example 2, among Examples of the present disclosure.

FIG. 3 is a photograph showing a ternary alloy phase layer ofZn/MgZn₂/Al formed on an inhibition layer in the photograph of FIG. 1.

FIG. 4 is a schematic view illustrating a plated steel material and awiping nozzle.

BEST MODE FOR INVENTION

A conventional zinc plating is solidified in a single Zn phase, whereasa Zn—Al—Mg-based zinc alloy plating coexist with a Zn phase, an alloyphase of Mg and Zn, and an Al phase. A plating structure may form a verycomplex plating structure, depending on physical and chemical conditionsof a surface of a base iron in accordance with trace elements,manufacturing processes, or the like, in a plating bath.

A Zn—Mg alloy phase in a plating structure of a Zn—Al—Mg-based zincalloy plating layer (hereinafter, a zinc alloy plating layer or aplating layer) may be made of various intermetallic compounds such asMgZn₂, Mg₂Zn₁₁, and the like, and hardness thereof may be Hv 250 to 300.In addition, an inhibition layer made of intermetallic compounds of Feand Al maybe formed at an interface between the plating layer and thebase iron. The intermetallic compounds of Fe and Al may include Fe₄Al₁₃,Fe₂Al₅, and the like. Since the intermetallic compounds also haverelatively high brittleness, cracks in the plating layer may be likelyto occur during physical deformation.

A zinc alloy plated steel material of the present disclosure may includea base iron, a zinc alloy plating layer formed on the base iron, and aninhibition layer formed between the base iron and the zinc alloy platinglayer.

A composition of the zinc alloy plating layer is not particularlylimited, but as a preferred example, may include, by weight, Mg: 0.5 to3.5%, Al: 0.5 to 20.0%, Zn as a residual component, and inevitableimpurities.

Magnesium (Mg) plays a very important role for improving corrosionresistance of a zinc-based plated steel material, and may effectivelyform a zinc hydroxide-based corrosion product on a surface of a platinglayer under a corrosive environment, to effectively prevent corrosion ofthe zinc-based plated steel material. In order to obtain the aboveeffects, the content thereof may be 0.5% by weight or more, and morepreferably 0.8% by weight or more. However, when the content thereof isexcessively high, there may be a problem that Mg oxidizing dross on asurface of a plating bath rapidly increases. In order to prevent theproblem, the Mg may be 3.5% by weight or less, and more preferably 2.0%by weight or less.

Aluminum (Al) suppresses the formation of the Mg oxide dross in theplating bath, and may react with Zn and Mg in the plating bath to form aZn—Al—Mg-based intermetallic compound, to improve corrosion resistanceof the plated steel material. In order to obtain the above effects, thecontent thereof may be 0.5% by weight or more, and more preferably 0.8%by weight or more. However, when the content thereof is excessivelyhigh, weldability and phosphatizing property of the plated steelmaterial can be deteriorated. In order to prevent the problem, the Almay be 20.0% by weight or less, and preferably 6.0% by weight or less.In addition, in order to promote solidification behavior of the bath,the Al may be more preferable 3.0% by weight or less.

Zn as a residual component and inevitable impurities may be included.

An inhibition layer may be formed between the zinc alloy plating layerand the base iron in the zinc alloy plated steel sheet. The inhibitionlayer may be composed of an intermetallic compound of Fe and Al (ex.,Fe₄Al₁₃, Fe₂Al₅, and the like). The inhibition layer may be composed offine grains, but may have brittleness when the grains have relativelycoarse shape. Therefore, when an external stress is added to the steelsheet, the inhibition layer may be destroyed, to deteriorate corrosionresistance due to peeling or cracking in processing of the platinglayer. Therefore, a grain size of the inhibition layer may be 300 nm orless, and an average grain size of the inhibition layer may be 100 nm orless.

A ternary alloy phase layer of Zn, MgZn₂, and Al formed to have athickness of 2 μm or less may be formed on the inhibition layer. Asacrificial cathodic reaction may primarily initiate at an interfacebetween the base iron and the zinc alloy plating layer under a corrosiveenvironment. In a case in which the ternary alloy phase is formed aroundthe interface between the base iron and the zinc alloy plating layer,when a cross-section of a product is exposed to the corrosiveenvironment, effects by a sacrificial process may increase at theinterface, and may be then continuously maintained. This may be becauseZn, Mg, which are mainly involved in the sacrificial process, and Al,advantageous for forming a passivation film, may be concentrated onaround the interface between the plating layer and the base iron. Theternary alloy phase layer may be formed on the inhibition layer, and maybe formed at least 30 area %, based on the total area of the inhibitionlayer. However, when the ternary alloy phase layer is excessivelyformed, hardness of an upper portion of the plating layer may be reducedto deteriorate frictional properties of the plating layer. Therefore,the ternary alloy phase layer may be not to exceed 90 area %. As anexample of a method of confirming the ternary alloy phase layer, theremaybe a method of confirming by using a scanning electron microscope(SEM) or a transmission electron microscope (TEM), enlarging across-section in magnification. Another example of the above method mayinclude dissolving the plating layer with hydrochloric acid (HCl)aqueous solution, observing a surface of the plating layer, andobserving the ternary alloy phase layer remaining in an upper portion ofthe inhibition layer. When observing the cross-section, along a boundaryof the cross-section, a length of the ternary phase formed on theinhibition layer may be measured from the entire length of theinhibition layer.

When the ternary alloy phase layer of Zn, MgZn₂, and Al is formed tohave a thickness exceeding 2 μm on the inhibition layer, effects by thesacrificial process around the interface between the base iron and thezinc alloy plating layer may be reduced, and effects of improvingcorrosion resistance of the cross-section may be also reduced.Therefore, it may be important to control a material state or coolingconditions such that a thickness of the ternary alloy phase layer doesnot exceed 2 μm.

The zinc alloy plating layer may include a Zn phase, an alloy phase ofMg and Zn (ex., MgZn₂, Mg₂Zn₁₁, and the like), an Al phase, and thelike. In a microstructure observed in the surface of the zinc alloyplating layer of the present disclosure, the Zn phase may include 15 to90 area % of the surface of the zinc alloy plating layer. Themicrostructure appearing in the surface of the plating layer may be veryclosely related to surface properties of the plating layer. When a ratioof the Zn phase in the surface of the plating layer is relatively small,there may be a problem that color of a plated surface becomes relativelydark due to Mg oxidation during long-term storage of the plated steelsheet. Therefore, the Zn phase in the surface of the plating layer maybe 15 area % or more. When a ratio of the Zn phase exceeds 90 area %,excessive cooling may be required so that productivity may bedeteriorated, which is not preferable.

The zinc alloy plating layer may include various phases as describedabove, and the Zn phase and the MgZn₂ phase thereamong may include abinary phase having a lamellar structure. In the zinc alloy platinglayer of the present disclosure, an average thickness of each of the Znphase and the MgZn₂ phase in a width direction, in the lamellarstructure of the Zn phase and the MgZn₂ phase included in the zinc alloyplating layer, may be 1.5 μm or less. Since the MgZn₂ phase may be morebrittle, compared to the Zn phase, when the lamellar structure is formedto be coarse, there may be relatively high possibility of destruction byexternal stress. Therefore, in the lamellar structure of the Zn phaseand the MgZn₂ phase formed from the surface of the plating layer, theaverage thickness of each of the Zn phase and the MgZn₂ phase in thewidth direction may be 1.5 μm or less (excluding 0). The lamellarstructure of the Zn phase and the MgZn₂ phase included in the zinc alloyplating layer may be a lamellar structure present up to 70 area % of theplating layer on the surface of the zinc alloy plating layer. Thethickness in the width direction may be determined by measuring at least10 locations of the lamella structure present in the plating layer, andcalculating an average value thereof.

Hereinafter, an embodiment of a method for manufacturing a zinc alloyplated steel material of the present disclosure will be described indetail. The method for manufacturing the zinc alloy plated steelmaterial of the present disclosure may include preparing a base iron;immersing the prepared base iron into a plating bath to plate the baseiron; and wiping to control a thickness a plating layer and thencooling.

In the preparing the base iron, it is desired to first make a metalstructure of a hot rolled steel material uniform. An average grain sizeof the hot rolled steel material may be 1 to 100 μm. In this case, agrain of the hot rolled steel material may be in a surface layer portion(within ⅛ or less of the total thickness from the surface). In a case inwhich non-uniformity of a structure of the hot rolled steel material,especially a surface structure of the hot rolled steel material isgenerated, uniform formation of the inhibition layer may be difficult,due to diffusion of non-uniformity of a surface shape during coldrolling and diffusion of non-uniformity of Fe from the base ironrequired for formation of the inhibition layer. The ternary phase to beformed in an upper portion of the inhibition layer may be also formednon-uniformly to deteriorate corrosion resistance in a cross-section. Tothis end, the average grain size of the hot rolled steel material may be1 to 100 μm. The grain size of the hot rolled steel material may bepreferably 1 to 50 μm, and more preferably 5 to 30 μm.

When the grain size of the hot rolled steel material is less than 1 μm,it maybe advantageous for securing strength, but surface roughness dueto the grain during cold rolling may be increased. Further, when thegrain size exceeds 100 μm, it may be advantageous in terms of shapehomogenization, but an excessive increase in hot rolling temperature maycause scale defects, and product manufacturing costs may increase. Anexample of a method for obtaining the grain size of the hot rolled steelmaterial may include maintaining hot rolling temperature at least 800°C. or higher, or increasing coiling temperature to 550° C. or higherafter hot rolling.

In preparing a cold rolled steel material by cold rolling the hot rolledsteel material, surface roughness (Ra) of the cold rolled steel materialmay be 0.2 to 1.0 μm, and steepness may be 0.2 to 1.2.

The surface roughness may be determined according to pressure of a rolland a surface shape of the roll, when the roll rolls the material. Whenthe surface roughness exceeds 1.0 μm, a non-uniform inhibition layer maybe formed when forming the plating layer, and non-uniformity formationbetween phases in the plating layer may increase. When the surfaceroughness is less than 0.2 μm, surface friction coefficient may decreaseto slip the steel material into the roll.

The measurement of the steepness may be a method of measuring a degreeof bending of a steel material having a width of 1 m or more and alength of 2 m or more, after placing the steel material, to closelyadhere a surface of the steel material to a surface plate having a flatsurface. A height (H) of the bending is divided by a wavelength (P) ofthe bending, and, the divided value is then expressed as the product of100. That is, the steepness may be expressed by a formula of height(H)/wavelength (P)×100. The lower the steepness, the higher the flatnessof the steel material. When the steepness exceeds 1.2, the degree ofbending of the steel material may be relatively large, which causes adeviation in surface flow when the steel material passes through theplating bath. Therefore, formation of the inhibition layer andhomogenization of the plating layer may be adversely affected. The lowerthe steepness is, the more advantageous. As an example, in order tomanage the steepness to less than 0.2, there may be a proposed method toslow down a speed of cold rolling, but the proposed method is notpreferable due to its excessive process costs.

A method for controlling surface roughness and steepness in anappropriate range is not limited thereto. A reduction ratio may be setto be within a range of 2 to 5% in a last rolling operation of coldrolling. Also, appropriate tension may be added to the steel sheetduring rolling. In addition, as an example for imparting surfaceroughness, plasma treatment may be performed on a surface of the steel.For example, in the cold rolling, since a final shape may be determinedby a roll in the last rolling operation, the reduction ratio may be 5%or less. In a case of a sheet having a thickness of 0.5 mm, thereduction ratio may be set to be 2% or more, to reduce overload of shearrolling.

Meanwhile, the cold rolled steel material as described above may beannealed at a temperature of 600 to 850° C., as necessary. At the timeof the annealing, a gas containing 1 to 10% by volume of hydrogen (H₂)in nitrogen (N₂) may be used. When a concentration of the hydrogen isless than 1% by volume, it may be difficult to reduction an oxide in asurface of the steel. When a concentration of the hydrogen exceeds 10%by volume, its manufacturing costs may increase. Therefore, the hydrogenmay be 1 to 10% by volume of the gas.

As dew point temperature in an atmosphere of the annealing differs, notonly proportions of components constituting an oxide film formed on thesurface of the base iron may be different, but also an internaloxidation rate may be different. Therefore, the dew point temperaturemay be managed in a range of −60 to −10° C. When the dew pointtemperature is less than −60° C., it is not preferable because excessivecosts in managing purity of a raw gas may be incurred. When the dewpoint temperature exceeds −10° C., reduction of contaminants on thesurface of the base iron may not be achieved well, and an oxide filmsuch as B, Mn, or the like, which may be a trace element or impuritycontained in the steel, maybe formed to deteriorate plating wettability.

A zinc alloy plated steel material may be manufactured by a platingprocess in which the base iron prepared as above is immersed into andwithdrawn from a plating bath. The plating bath may include, by weight,Al: 0.5 to 20.0%, Mg: 0.5 to 3.5%, Zn as a residual component, andinevitable impurities. Each of the components maybe not different fromthose described in the zinc alloy plating layer described above.

An inhibition layer of Fe and Al may be formed on the surface of thebase iron immersed in the plating bath, a plating layer includingcomponents, similar to the components of the plating bath, maybe formedon the inhibition layer, and a steel sheet may be withdrawn from theplating bath. In this case, temperature of the plating bath may bewithin a range of 430 to 500° C. When the temperature of the platingbath is less than 430° C., even though the base iron is immersed intothe plating bath, decomposition of the oxide on the surface of the baseiron maybe not smoothly performed, which may be disadvantageous in theformation of the inhibition layer. When the temperature of the platingbath exceeds 500° C., it is not preferable because dross on the surfaceof the plating bath may occur and Mg oxidation may occur significantly.

The plating process may use a process of depositing componentsindividually in the plating bath, and a continuous hot dip platingprocess in which a steel material (particularly, a steel sheet) iscontinuously passed through the plating bath to form a plating layer. Inthe continuous hot dip plating process, a velocity of passing of thesteel material may be 60 to 200 MPM (a passing distance per minute,meter per minute). When the velocity of the passing is less than 60 MPM,product productivity may decrease. When the velocity of the passingexceeds 200 MPM, non-uniformity between the inhibition layer and theplating layer may occur.

In the zinc alloy plated steel material withdrawn from the plating bath,a thickness of the plating layer may be adjusted by a wiping nozzle,called an air knife, in an upper portion of the plating bath, and acooling operation may be then performed. The wiping nozzle may spray airor an inert gas to adjust the thickness of the plating layer. Whenpassing through the wiping nozzle, temperature of the plating layer andthe steel material, and adjustment of the wiping nozzle may affectstructure formation of the plating layer.

FIG. 4 is a schematic view illustrating a plated steel material and awiping nozzle. Referring to FIG. 4, the present disclosure may satisfy aworking index of 0.5 to 40 determined by the following relationship 2,defining gas injection pressure in the wiping nozzle (P), a distancebetween the wiping nozzle and the steel material (D), a slot thicknessof the wiping nozzle (t), a velocity of a passing of the steel material(S), and temperature of a plating bath (T):

$\begin{matrix}{{{Working}\mspace{14mu} {index}} = {\frac{\left\{ {\left( \frac{P}{D} \right)*t} \right\}}{S}*\left( {T - 400} \right)}} & \left\lbrack {{Relationship}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Where P denotes a pressure of a wiping gas (KPa), D denotes a distancebetween the wiping nozzle and a plated steel material (mm), t denotes athickness of the wiping nozzle (mm), S denotes a velocity of a passingof the steel material (MPM), and T denotes a temperature of the platingbath (° C.).

The working index maybe a shape factor of the base iron before plating,and may be suitable for forming a desirable plating structure, when aplating layer is prepared, in a state in which surface roughness (Ra) is0.2 to 1.0 μm and steepness is 0.2 to 1.2. That is, a fine lamellarstructure in the plating layer fine may be made, and at the same time,formation of a ternary alloy phase directly in the inhibition layer maybe facilitated at an interface between the plating layer and the baseiron. When the working index is less than 0.5, a fraction of the Znphase of the surface of the plating may be reduced to easily discolorthe surface of the plating, and the lamellar structure may be coarse tooccur cracking of the plating during processing. When the working indexexceeds 40, defects such as flow patterns may occur on a surface of theplating layer. Therefore, the working index defined by the relationship2 may be 0.5 to 40.

After the wiping process, the plated steel material may be cooled, andthe cooling operation may satisfy the following relationship 1:

0.7Vc≤Vc′≤1.5Vc   [Relationship 1]

where Vc is an average cooling rate until end of solidification of aplating layer immediately after wiping, and Vc′ is an average coolingrate until start of solidification of the plating layer immediatelyafter wiping.

As a factor influencing structures and growths of phases in the platinglayer, in order to obtain a desirable structure, a ratio (Vc′/Vc) of anaverage cooling rate until start of solidification of the plating layerimmediately after wiping (Vc′) to an average cooling rate until end ofsolidification of a plating layer immediately after wiping (Vc), may be0.7 to 1.5.

[Mode for Invention]

Hereinafter, examples of the present disclosure will be described indetail. The following examples are only for understanding the presentdisclosure and are not intended to limit a scope of the presentdisclosure. This is because the scope of the present disclosure may bedetermined by contents described in the claims and contents reasonablyinferred therefrom.

EXAMPLE

Cold rolled steel sheets having a thickness of 0.8 mm were used as baseirons to prepare base steel sheets for an automotive exterior including,by weight, 0.03% of C, 0.2% of Si, 0.15% of Mn, 0.01% of P, and 0.01% ofS. In this case, values for surface roughness (Ra) and steepness of eachof the base steel sheets are shown in Table 1. Cold rolled steel coilswere continuously immersed in and withdrawn from a Zn—Al—Mg alloyplating bath, and were subject to wiping and cooling operations toprepare zinc alloy plated steel sheets. Specific conditions used in thiscase are shown in Table 1.

Components of a plating layer of each of the prepared zinc alloy platedsteel sheets, spraying pressure of a wiping nozzle (P), a distancebetween the wiping nozzle and the steel sheet (D), a slot thickness ofthe wiping nozzle (t), a velocity of passing of the steel material (S),and plating bath temperature (T) are reflected in the conditions shownin Table 1 below, to calculate values for a working index defined byrelationship 2 above, and show the calculated values for working indexin Table 1 together.

An area fraction of a Zn phase observed in a surface of the zinc alloyplated steel sheets prepared as described above, a distance between Znand MgZn₂ phases of a lamellar structure in a width direction, presentup to 70% of a thickness of a plating layer from the surface of theplating layer, and area fraction of a ternary alloy phase layer ofZn/MgZn₂/Al having a thickness of 2 μm or less, included in aninhibition layer, were measured, and the measured values were shown inTable 2 together.

In addition, in order to confirm properties of each of the zinc alloyplated steel sheets, surface properties, and corrosion resistance ofcross-sectional and processed portions of each of the zinc alloy platedsteel sheets were evaluated, and the evaluated results were shown inTable 2. Regarding the surface properties, a flow pattern and a degreeof surface discoloration were measured, the degree of surfacediscoloration was evaluated by measuring a color difference of a surfaceof each samples, standing each of the samples at a temperature of 50° C.and humidity (95%) for 24 hours, and measuring then the color differenceof each of the samples again, to evaluate values (dE) with reducedrespective brightness value. Regarding corrosion resistance of each ofthe cross-sectional and processed portions, Cyclic Corrosion Testspecified in ISO TC 156 was performed for each of the samples. Thenumber of cycling occurrence of red rust (cycle number) in thecross-sectional portion of each of the samples, determined by thecorrosion test, and the number of cycling occurrence of red rust (cyclenumber) in the processed portion of each of the samples, determined bybending each of the samples to 180° and performing the corrosion test tomeasure the number of cycling occurrence of red rust in the bent area,were recorded.

TABLE 1 Velocity Air Plating of Knife- Layer Steel Steel Passing PlatingAir Steel Nozzle Average Components Sheet Sheet of the Bath Knife SteetSlot Working Cooling Classi- (wt %) Ra Step- steel Temp. PressureDistance Thickness Index Rate fication Mg Al (μm) ness (MPM) (° C.)(Kpa) (mm) (mm) Value (Vc′/Vc) *IE1 1.2 1 0.4 0.2 170 455 35 15 2 1.50.7 IE2 1.6 2.5 0.3 0.7 120 455 65 10 1.5 4.5 1.1 IE3 1.5 1.5 0.5 0.8 80430 75 7 2 8.0 1.3 IE4 3 2.5 0.8 1.0 65 470 70 5 2.5 37.7 1.0 IE5 3 60.6 1.2 65 425 65 12 1.5 3.1 1.2 IE6 3 20 0.3 0.4 80 490 55 12 2 10.31.5 **CE1 1.6 1.6 0.4 1.3 55 470 90 4 1.5 43.0 0.8 CE2 1.3 1.6 1.3 1.5180 450 20 20 0.8 0.2 0.5 CE3 3 3 0.8 1.3 160 410 40 17 1.5 0.2 0.4 CE43 6 1.1 1.4 75 460 90 6 3 36.0 1.8 *IE: Inventive Example, **CE:Comparative Example

TABLE 2 Evaluation of Properties Number of cycling Number Plating LayerStructure Occurrence of cycling The Zn/MgZn₂/Al of Red Occurrencepresence Distance Tertiary Rust in of Red of Flow Surface between AlloyCross- Rust in Pattern Zn Zn—MgZn₂ Phase Color Sectional ProcessedClassi- Defect Phase Phases Layer Difference Portion Portion fication∘(/x) (area %) (Width, μm) (area %) (dE) (Cycle No.) (Cycle No.) *IE1 x75 0.5 65 3 55 35 IE2 x 56 0.7 30 3 60 35 IE3 x 15 1.4 45 2 65 45 IE4 x30 1.0 55 2 50 40 IE5 x 45 0.8 35 2 65 35 IE6 x 60 0.4 38 2 50 45 **CE1∘ 13 1.8 25 5 45 20 CE2 x 7 1.7 30 6 35 25 CE3 x 10 2.0 15 5 45 25 CE4 ∘12 2.2 5 5 30 25 *IE: Inventive Example, **CE: Comparative Example

FIG. 1 is a photograph showing a cross-section of a plating layer ofInventive Example 3. As shown in FIG. 1, it can be seen that a platinglayer was provided on a base steel plate 11, a Zn single phase 12 and alamella structure 13 was formed in the plating layer, and the lamellastructure 13 was finely formed to reduce occurrence of cracks duringprocessing. FIG. 3 shows an interface between the base steel sheet 11and the Zn single phase 12, shown in FIG. 1, and it can be seen that aninhibition layer 14 and a ternary alloy phase of Zn/MgZn₂/Al wereformed. Specifically, it can be seen that an MgZn₂ phase 15, an Al phase16, and a Zn phase 17 were formed. FIG. 2 is a photograph showing across-section of a plating layer of Comparative Example 2, and it can beseen that a lamellar structure 23 was formed to be coarse. Therefore, itcan be seen that cracks may be easy occurred during processing.

From the results of Table 2 and FIGS. 1 to 3, in the Inventive Examplessatisfying the defined conditions of the present disclosure, excellentsurface properties maybe secured and excellent corrosion resistancemaybe secured, even in the cross-sectional and processed portions.

While example embodiments have been shown and described above, it willbe apparent to those skilled in the art that modifications andvariations could be made without departing from the scope of the presentdisclosure as defined by the appended claims.

1. A zinc alloy plated steel material having excellent surface qualityand corrosion resistance, comprising: a base iron; a zinc alloy platinglayer formed on the base iron; and an inhibition layer formed betweenthe base iron and the zinc alloy plating layer, wherein a Zn phase of asurface of the zinc alloy plating layer comprises 15 to 90 area %, andthe inhibition layer includes a ternary alloy phase layer of Zn/MgZn₂/Alhaving a thickness of 2 μm or less on the inhibition layer, wherein theternary alloy phase layer comprises 30 to 90 area % of a surface of theinhibition layer.
 2. The zinc alloy plated steel material havingexcellent surface quality and corrosion resistance according to claim 1,wherein the zinc alloy plating layer comprises a lamellar structure ofthe Zn phase and an MgZn₂ phase, wherein an average thickness of each ofthe Zn phase and the MgZn₂ phase in a width direction is 1.5 μm or less.3. The zinc alloy plated steel material having excellent surface qualityand corrosion resistance according to claim 1, wherein a grain size of aFe—Al based intermetallic compound in the inhibition layer is 300 nm orless.
 4. The zinc alloy plated steel material having excellent surfacequality and corrosion resistance according to claim 1, wherein the zincalloy plating layer comprises, by weight, Mg: 0.5 to 3.5%, Al: 0.5 to20.0%, Zn as a residual component, and inevitable impurities.
 5. Amethod of manufacturing a zinc alloy plated steel material havingexcellent surface quality and corrosion resistance, comprising:preparing a base iron; immersing the base iron into a zinc alloy platingbath containing Mg and Al to plate the base iron; and wiping the platedbase iron, and then cooling, wherein the cooling satisfies the followingrelationship 1:0.7Vc≤Vc′≤1.5Vc   [Relationship 1] where Vc is an average cooling rateuntil end of solidification of a plating layer immediately after wiping,and Vc′ is an average cooling rate until start of solidification of theplating layer immediately after wiping.
 6. The method of manufacturing azinc alloy plated steel material having excellent surface quality andcorrosion resistance according to claim 5, wherein the preparing thebase iron comprises: preparing a hot rolled steel material having asurface layer portion having a grain size of 1 to 100 μm; and coldrolling the hot rolled steel material to prepare a cold rolled steelmaterial having a surface roughness of 0.2 to 1.0 μm and a steepness of0.2 to 1.2.
 7. The method of manufacturing a zinc alloy plated steelmaterial having excellent surface quality and corrosion resistanceaccording to claim 5, wherein a composition of the plating bathcomprises, by weight, Mg: 0.5 to 3.5%, Al: 0.5 to 20.0%, Zn as aresidual component, and inevitable impurities.
 8. The method accordingto claim 5, wherein the plating and wiping satisfy a working index of0.5 to 40 represented by the following relationship 2: $\begin{matrix}{{{Working}\mspace{14mu} {index}} = {\frac{\left\{ {\left( \frac{P}{D} \right)*t} \right\}}{S}*\left( {T - 400} \right)}} & \left\lbrack {{Relationship}\mspace{14mu} 2} \right\rbrack\end{matrix}$ where P denotes a pressure of a wiping gas (KPa), Ddenotes a distance between the wiping nozzle and a plated steel material(mm), t denotes a slot thickness of the wiping nozzle (mm), S denotes avelocity of passing of the steel material (meters per minute, MPM), andT denotes a temperature of the plating bath (° C.).
 9. The method ofmanufacturing a zinc alloy plated steel material having excellentsurface quality and corrosion resistance according to claim 5, wherein atemperature of the plating bath is 430 to 500° C.
 10. The method ofmanufacturing a zinc alloy plated steel material having excellentsurface quality and corrosion resistance according to claim 5, whereinin the plating process, a velocity of a passing plate is 60 to 200 MPM(meters per minute).